25W x with LM1875 and 2SA1943 / 2SC5200

The circuit is shown in Figure 1. The chip IC uses the LM1875 of the American NS company. It has a soft tone and low distortion (0.015%). It is quite famous at low power and is widely praised. The output tube adopts the relatively warm and soft Toshiba high-power pair tube 2SA1943, 2SC5200 (VCM = 180V, ICM = 12A, PCM≥120W, fT = 30MHz). The principle of this circuit is as follows: when the audio signal is input to the positive phase input terminal of IC through C1 and R1, the voltage of the power supply resistors R4 and R5 connected to the positive and negative power supply of the IC will change with the signal. R5 is the bias resistance of the power tube. When the signal reaches the required amplitude, the power tubes VT1 and VT2 are turned on, so that the power of the LM1875 is expanded. When using ± 25V power supply, the output power can reach more than 30W under 8Ω load.



The printed board diagram is shown in Figure 2 (two channels are required for two channels). Assembly points: Because the negative power supply of the IC is connected to the metal cap, an insulation sheet and a sufficient amount of silicone grease must be added between the IC and the heat sink The heat sink should be genuine and should not be hot during long hours of work, otherwise the heat sink should be increased. Since the quiescent current of the IC is about 70mA, the values ​​of R4 and R5 determine the conduction point of the power tube. In this circuit, when the IC output current is close to 1A, the power tube is turned on. R4 and R5 use a 3W non-inductive resistor. Imported genuine power tubes are selected and matched, and the error is as small as possible (within 3%), which is especially important for the clarity of music. The coil L1 at the output end is densely wound 10 turns on the 3W non-inductive winding resistor R10 with φlmm enameled wire. The power supply part (see Figure 3 and Figure 4) uses 150W dual 18V high-quality toroidal transformer, 4 filter capacitors of 35V / 4700μF, two 35V / 100μF, two 100V / 0.1μF, and 4A fuse tubes FUSE1 and FUSE2.

Technical area detailed analysis of Doherty power amplifier design load traction principle (top) detailed analysis of Doherty power amplifier design how to improve efficiency (lower) voltage follower input and output error analysis lm386 power amplifier energization will produce noise causes and treatment methods analysis class d Solve the effect of power amplifier on emi

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